1. Field of the Invention
The present invention relates to an interface circuit that is suitable for use in digital audio equipment and digital video equipment. It also relates to an optical disk (disc) manufacturing system for manufacturing optical disks such as compact disks and digital video disks, and more particularly to a manufacturing system that can manufacture optical disks that record digital waveform data faithfully with respect to the original sound or image, without the influence of such non-code components as jitter components and waveform distortion components (ripple components).
2. Description of the Related Art
FIG. 1 is a block diagram that shows an example of the case in which an interface circuit of the past is applied to, for example, a compact disk (CD) player.
The digital signal processing unit 61 is provided with a servo circuit 63, which controls the rotational drive system of a CD 62, a digital signal processing circuit 64, which processes signals read from the CD 62, and a quartz oscillator 65 that serves as a synchronization reference.
The interface circuit 66 is formed by a transmitting-side interface circuit 66a within the digital signal processing unit 61 and a receiving-side interface circuit 66 within an analog signal processing unit 67. The transmitting interface circuit 66a and the receiving-side interface circuit 66b are joined by means of an optical transmission element.
The analog signal processing unit 67 is provided with a digital filter 68 and a digital-analog (D/A) converter 69.
As shown in FIG. 1, the digital signal processing unit 61 and the analog signal processing unit 67 are of separate construction (D/A-separated construction). This is done to prevent electrical noise that is generated in the servo circuit 63 or the digital signal processing circuit 64 from influencing the analog signal processing unit 67, as this can adversely affect the sound quality. When a D/A-separated system is housed in one and the same enclosure, great care is taken with respect to unwanted radiation.
In general, the power supply of the analog signal processing unit 67 is kept separate from the digital signal processing unit 61, as a measure to prevent the deterioration of sound quality by the power supply ground line.
Having taken the above-noted measures, a digital signal is transmitted from the digital signal processing unit 61 to the analog signal processing unit 67, with optical transmission, which features total electrical isolation and no unwanted radiation, being used in both separate and single-enclosure implementations.
However, the adverse affect on sound quality that the digital signal processing unit 61 has on the analog signal processing unit 67 is still not entirely eliminated, and optical transmission is accompanied by the following problems.
(a) In the process of sending a digital signal from the digital signal processing unit to the analog signal processing unit, a jitter component and a waveform distortion component (a ripple component) are added to the digital signal waveform, these representing a deterioration of the digital signal waveform.
(b) A jitter component that is generated in the digital signal processing unit, which is the cause of a deterioration in sound quality, is transmitted to the analog signal processing unit via the digital signal transmission.
One measure taken to solve the above-noted problems (a) and (b), is that of using a clock having the accuracy of a quartz element is used in the digital signal processing unit to perform resampling of the digital signal immediately before transmission. Another measure to solve the above-noted problems is that of compensating the variation of pulse width in the optical transmission in the analog signal processing unit, and using two stages of PLLs to improve the accuracy of the timing clock.
An additional method is that of moving the quartz oscillator, which serves as the synchronization or timing reference from its usual position in the digital signal processing unit to the analog signal processing unit, and using the resultant synchronization signal to more reliably establish synchronization of the digital signal processing unit, and to resample readout data using a clock of quartz oscillator accuracy in the analog signal processing unit, thereby improving the accuracy of the digital signal.
While the above measures do have some effect, it is intrinsically not possible to eliminate causes of sound quality deterioration (jitter and waveform distortion components) that are added in the process of digital signal transmission from the disk to the analog signal processing unit.
The jitter components and waveform distortion components are non-correlated components, which are not correlated to the original audio signal (the signal before being recorded digitally on a CD, for example). In contrast to these non-correlated components, harmonic distortion components of the analog signal can be referred to as correlated components. Because the level of a non-correlated component perceived by the human ears is extremely high, the annoyance imparted audible sound quality by a non-correlated component is greater than that from a correlated component.
In a digital signal, even if the binary (0 and 1) coding itself remains the same, these non-correlated components cause the audio quality to change.
FIG. 2 shows a transmitted digital signal, in which (a) is a digital signal that is transmitted from a digital signal processing unit via an interface circuit to an analog signal processing unit, (b) is the original coding information that is read from the disk, and (c) shows the jitter and waveform components that are generated within the digital signal processing unit.
The original coding information shown in FIG. 2, (b) has the jitter component and waveform distortion component (non-correlated components) that are shown in FIG. 2, (c) superimposed on it, thereby making the transmitted signal (shown in FIG. 2, (c)), which is transmitted to the analog signal processing unit.
In this manner, once the non-correlated components are added to the digital signal, they cannot be removed by digital transmission that is used for the purpose of separating the digital and analog circuitry. Although an optical fiber is immune to the superimposition of external noise, because it does not have the function of removing non-correlated components that are already included in a digital signal, these non-correlated components are transmitted along with the digital signal, so that there is almost no effect of improving the non-correlated distortion.
Additionally, once these non-correlated components are transmitted, they intrude into the ground and power supply lines within the analog signal processing unit, so that while subsequent waveform shaping or the like can make an apparent improvement in the appearance of the digital waveform, the non-correlated components pass directly through the digital-analog converter, and act to change the analog quality.
In the past, one known recording method that enables faithful playback of a recorded original sound was that of direct cutting. This direct cutting method is that of using the sound from a performance as either an analog or a digital signal for immediate direct recording onto a recording medium. Using the direct cutting method, because the original sound can be directly recorded onto a recording medium, it is possible to faithfully record the original sound onto a recording medium and play back the sound therefrom, with almost no noise or deterioration of the sound quality.
To record using the above-noted direct cutting method, however, it is necessary either that a performer be brought to a location at which the direct cutting recording equipment is installed, or that the direct cutting recording equipment be brought to the location of the performance. Additionally, if a mistake occurs during a performance, because it is not possible to perform editing, such as having the performer continue the performance from the location of the mistake, the performer must start over from the beginning, this making the direct cutting recording method both troublesome and inconvenient.
The direct cutting method is currently considered to be the ideal recording method, and in practice an indirect recording method is used, wherein a primary recording of the original sound is first made (onto a recording medium known as a master tape or the like), the original sound information that is played back from this primary recording medium being subsequently recorded onto a secondary recording medium, this secondary recording medium being, for example, a mother stamper for a CD.
The above-described indirect recording method is currently used to produce CD mother stampers and the general method for doing so comprises a process whereby a CD mother stamper is formed, as shown in FIG. 3A, a production process whereby the primary recording of the original sound is made, as shown in FIG. 3B, and a manufacturing process whereby the original sound information is played back from the primary recording medium formed in the production process and this information is recorded onto a second recording medium.
The production process that is shown in FIG. 3A is performed, for example, in an audio studio, the performance of a performer being collected by the use of microphones 80 (or from a recording medium on which the performance has been recorded), the thus collected analog audio information being converted to digital data by means of an A/D converter 81. This audio data is then digitally recorded using a master recorder 82 onto a primary recording medium 83, such as a magnetic tape. The primary recording medium 83, onto which is recorded the performance of a performer, is then brought to a CD factory (CD pressing factory) as the master tape.
The manufacturing process that is shown in FIG. 3B indicates the processes at the CD pressing factory, whereby the master playback apparatus 85 plays back the audio data from the master tape (primary recording medium 83), this audio data being then supplied to the CD cutting apparatus 86. The CD cutting apparatus 86 shines a laser beam that is on/off controlled in accordance with the audio data from the master playback apparatus 85 onto a glass disk onto which a photosensitive material (photoresist) has been coated, so as to create pits therein which correspond to this audio data, this process being known as laser cutting. Then pits that are formed on the recording master are transferred by plating the glass disk with nickel, thereby forming the mother stamper, which is a nickel stamper electrocasting. By doing this, the audio data that was recorded on the master tape, which is the primary recording medium, is recorded onto the mother stamper, which serves as the secondary recording medium.
This mother stamper is passed through an inspection process, after which it is mounted to a die. The die is used to injection mold an acrylic resin so as to form transparent acrylic disks, onto which aluminum is vacuum deposited, followed by the application of a protective plastic film to form the CD disk.
In the above-noted processes, the original sound is indirectly digitally recorded on the secondary recording medium via a primary recording medium. Because the information is coded digital information (1 and 0 data), it can be envisioned that, as long digital recording is done, the audio quality will not change. In actuality, however, in the process of propagating the audio information, as shown in FIG. 4, components other than the digital code, such as a ripple component (AC component) and a jitter component (waveform fluctuations) and the like are superimposed thereon, these non-code components being a cause of a change in the audio quality in the recording system in, as described above, recording is performed indirectly, even if digital recording is employed.
More specifically, in the production process that is shown in FIG. 3A, noise enters the A/D converter 81 from the ground 82a of the master recording apparatus 82, via the earth and the ground 81a of the A/D converter 81, or noise enters the A/D converter 81 and master recording apparatus 82 via the power supply lines 81b and 82b of the A/D converter 81 and master recording apparatus 82, respectively, and further noise enters the AID converter 81 via connecting line 84, which connects the A/D converter 81 and the master recording apparatus 82, the result being the formation of a noise loop such as indicated by the broken line in FIG. 3A. The result of this noise loop is that, when the analog audio signal from the microphone 80 is digitized by the A/D converter 81, the reference voltage, for example, for this analog-to-digital conversion varies due to the above-noted noise, causing the occurrence of an error between the digitized audio data and the original sound. Therefore, at this production process the audio data recorded on the master tape already includes an error with respect to the original sound, this error being recorded as part of the audio data.
In the same manner, in the manufacturing process shown in FIG. 3B, noise enters the CD cutting apparatus 86 from the ground 85a of the master playback apparatus 85, via the earth and the ground 86a of the CD cutting apparatus 86, or noise enters the master playback apparatus 85 and CD cutting apparatus 86 via the power supply lines 85b and 86b of the master playback apparatus 85 and CD cutting apparatus 86, and further noise enters the CD cutting apparatus 86 from the master playback apparatus 85, via the connection line 87, which connects the master playback apparatus 85 and the CD cutting apparatus 86, the result being the formation of a noise loop such as indicated by the broken line in FIG. 3B. The result of this noise loop is that, when audio data that is played back from the master tape by the CD cutting apparatus 86 is recorded on the glass master disk, because of the above-noted noise there the audio data that is recorded has a further error introduced with respect to the original sound (the overall error now being the production process error and the manufacturing process error).
Because this error with respect to the original sound appears as an error in the pit lengths that are formed on the mother stamper, a situation that is undesirable, since the CDs produced by this mother stamper have audio that is different from the original sound.
To solve the above-described problems, the inventors of the present invention proposed the interface circuit that is disclosed in the Japanese Patent Application Serial No. 61-136058 (Japanese Patent Application Publication No. H5-18496; Patent No. 1811632).
According to the above-noted circuit, in a receiving interface circuit, the logic of the transmitted digital signal is detected with a timing that does not include a jitter component of the transmitted digital signal, simultaneously with which the waveform distortion component is removed from the transmitted digital signal, enabling the playback of the transmitted digital signal, based on the detected transmitted digital signal logic.
The above-noted proposed interface circuit is suitable for application to, for example, a studio-type audio system.
In this type of system, for example, if a high-fidelity digital signal having no waveform distortion or jitter is produced of a vocal or instrumental sound, this being recorded onto a prescribed recording medium, and it is possible to playback a digital signal with no waveform distortion or jitter under the same conditions as when the signal was recorded, it is possible to verify what kind of digital sound was recorded, making this circuit suitable for use in a studio recording system.
However, with the configuration of the interface circuit that was proposed by the inventors of the present invention, it is possible to eliminate waveform distortion and jitter with respect to one side, the configuration not enabling the removal of waveform distortion and jitter with respect to the other side, making it impossible to play back a signal with the same conditions on both sides of the transmission path.
That is, it is possible to supply a digital signal from the transmitting side to the receiving side that does not have waveform distortion and jitter, but if this noise-free signal is returned to the transmitting side, waveform distortion and jitter are mixed therewith in the transmission process, making it impossible to transmit a digital signal that is free of noise.
The present invention was made to solve the above-noted problem, and has as an object the provision of an interface circuit that enables the transmission of a digital signal without waveform distortion and jitter in both the transmitting and receiving directions.
A further object of the present invention is to provide an optical disk manufacturing system which makes use of the advantage of the indirect recording method and enables manufacture of an optical disk onto which is faithfully recorded an original sound.
To achieve the above-noted objects, the first aspect of the present invention provides a interface circuit that is configured so as to enable mutual digital signal transmitting and receiving between a first interface section and a second interface section, making use of an optical, acoustic, or electromagnetic linking means, wherein for the purpose of removing a jitter component and a waveform distortion component from the digital signal, these interface sections comprise:
a control driver which is supplied with a driver control signal, and by which the digital signal can be placed either in the on or the off operating state for an extremely short period of time in comparison with the duration time of one bit of the digital signal, this being done at a timing that does not include a jitter component;
a receiving section which, during a period of time in which an electrical current flows in a transmission section of the first and second interface sections, performs code detection for only an extremely short period of time with an operational timing that is the same as the control driver;
an output circuit that outputs a received digital signal, this output circuit being supplied with the output signals of these receiving sections as data, and with a read clock signal having the same timing as the driver control signal; and
a timing signal generator to which is supplied a base signal that serves as the synchronization reference signal for the first and second interface sections, and which generates the driver control signal that does not contain a jitter component and the read clock.
The second aspect of the present invention is an optical disk manufacturing system that has, as a means of solving the above-described problems, an interface means that outputs the digital information as a waveshaped waveform. This interface means detects the digital information code based on prescribed synchronization information, and reproduces the digital information based on the resulting code detection output.
Although the digital information includes such non-code components as ripple and jitter, by using the above-noted interface means it is possible to derive from this digital information from which these non-code components have been removed. For this reason, by recording this digital information onto a master recording medium, it is possible to form a master recording medium onto which is recorded digital information that is a faithful representation of the digital waveform of the original information. Further, by using this master recording medium to as the basis for forming a mother stamper and then using the mother stamper to manufacture CDs, it is possible to manufacture CDs onto which is recorded digital information that is a faithful representation of the digital waveform of the original information.